ASoC: wcd: ensure regulator is on during plug detection

To detect special headset we need MICBIAS at 2.7V,
so ensure that the required regulator is on before
going for special headset plugtype determination.

CRs-fixed: 676589
Change-Id: Ib18db2b11f18fc88fb67d60717ca06eafb2fc277
Signed-off-by: Yeleswarapu Nagaradhesh <nagaradh@codeaurora.org>